1. Field of the Invention
The present invention generally relates to a transfer apparatus. In particular, it relates to a transfer apparatus for linearly transferring a thin work such as a wafer and a glass substrate used in the fabrication process of semiconductor devices or liquid crystal display panels.
2. Description of the Related Art
A transfer apparatus provided with a linear moving mechanism for moving a work-holding hand along a linear path has a simpler structure and is less expensive than a jointed-arm robot. Thus, such a linear transfer apparatus is often used for carrying in or out a thin work (a wafer, a glass substrate, etc.) relative to a process chamber in manufacturing semiconductor devices or liquid crystal display panels, for example.
An example of a conventional linear transfer apparatus is disclosed in JP-A-2005-125479. The transfer apparatus disclosed includes a link arm mechanism supported by a rotary base. A hand for horizontally holding a work such as a substrate is mounted to an end of the link arm mechanism. The rotary base is mounted to a cylindrical lift base supported by the stationary base to be movable vertically. In accordance with the vertical movement of the lift base, the hand supported by the rotary base is brought to a predetermined height. When the rotary base rotates on the stationary base about a vertical rotation axis, the link arm mechanism rotates correspondingly. When the link arm mechanism pivots, the work held by the hand moves linearly within a horizontal plane. Thus, the work is transferred from a certain position to another position.
The conventional transfer apparatus includes lifting means for vertically moving the lift base, and this lifting means comprises two slide guide mechanisms and a single screw-feeding mechanism (see FIG. 21 of JP-A-2005-125479). The slide guide mechanisms facilitate the vertical slide movement of the lift base and arranged to be spaced from each other. Each of the slide guide mechanisms is made up of a vertically extending guide rail provided at the stationary base and a guide member provided at the lift base. The guide member is in sliding engagement with the guide rail. The screw-feeding mechanism applies driving force for the vertical movement to the lift base. The screw-feeding mechanism comprises a vertically extending screw shaft rotatably mounted to the stationary base and a nut member provided at the lift base. The nut member is screwed onto the screw shaft. When the screw shaft rotates, the lift base moves vertically with the nut member.
The transfer apparatus including the above-described linear moving mechanism may be used for carrying in or out a work relative to a process chamber in the process of manufacturing a semiconductor device or a liquid crystal display panel. Specifically, for instance, a vacuum transfer module may be disposed between an atmospheric transfer module and each process chamber, and the transfer of the work may be performed via the vacuum transfer module. The vacuum transfer module includes a transport chamber around which a plurality of process chambers are arranged, and a load lock connecting the atmospheric transfer module and the transport chamber to each other. The transfer apparatus operable in a vacuum is disposed in the transport chamber. The transfer apparatus performs operations such as receiving a work from the load lock, transferring a work into the transport chamber, transferring a work into any of the process chambers, receiving a processed work from a process chamber, and transferring a work into the load lock. A stage for placing a work is provided in the load lock. The transfer of a work is performed on the stage by a hand of the transfer apparatus.
In the transfer apparatus, the load of the hand and a work is applied to the lift base via the slide guide mechanism and the screw-feeding mechanism. When the work is positioned directly above the stationary base, the load applied to the slide guide mechanisms and that on the screw-feeding mechanism are substantially well-balanced, so that the vertical movement is performed properly. However, when the work is held at a location deviated from the position directly above the stationary base, biasing load or moment load is applied to the slide guide mechanism and the screw-feeding mechanism. In this case, due to the biasing load or the moment load, positional deviation in the vertical direction may occur in the slide guide mechanism and the screw-feeding mechanism. When the positional deviation occurs, the vertical movement of the lift base may not be performed smoothly or the hand may not be held horizontally. Further, in recent years, in accordance with an increase in size of works, there are demands for increasing the distance of the horizontal transfer movement. However, such an increase causes an increase in biasing load and moment load, which encourages the above-described disadvantage.